FAQs

Charging efficiencies

In this article, we will discuss so of the losses when power is converted or transformed or used. Our niche is the conversion of energy and with that there are losses. For example, a light bulb was designed to provide light. It does this by making a small filament of wire glow. The glowing generates the light that's wanted but also heat and that is a wasteful by-product of a light bulb.

With battery charging which is a chemical reaction, there are losses through the chemical conversions of electrons moving between plates and acids. These losses are minimalised with improvements in the technology with over 100 years in development. Losses in charging lead-acid vary from 12% for AGM batteries to about 20-25% for wet cell batteries. That means a 100Ah battery requires 112-125 Amps to recharge and store 100Ah of usable energy.

When you convert DC power from a battery into AC mains power using an inverter the equipment inside the inverter uses power and that accounts for a 5% loss in available power. The same happen when converting AC power into DC power, these devices are called power supplies, or chargers, or power rectifiers. Switch-mode supplies are typically used in all modern-day equipment to help reduce these inefficiencies but they need to be calculated and allowed for.

An example of this might be an off-grid solar system with a small inverter for charging a cellphone.

Solar panels generate DC power 18-20% efficient, that's run through a solar controller 95% into a battery for storage 85% efficient. The mains power inverter converts DC power into AC mains 95% and you connect your phone charger in here. The charger is only 90-95% efficient which then connects to your phone's Lithium battery. Let's just say here it's 99% efficient at charging. All in all, you have four pieces of equipment all with up to 10% losses so your generation of the panels needs to be almost twice the power you want to consume.

When using mains power or grid-tie to power your home but have batteries for backup energy there are losses. You also lose more power in converting them back from DC stored energy in the battery back into usable mains power. This highlights an issue with grid-tie and battery backup. Multiple conversions, the storage, use and generation all have efficiencies and losses.

In future articles, we'll discuss DC versions much like our DC to DC chargers. Direct DC Coupling in a renewable energy system and more.

Hardware differences for Grid Tie and Off Grid

With a grid-tie connection, the property uses mains power provided from the nationwide power grid as a secondary power source. It generates DC power from solar panels, sends that power through an inverter which converts it into mains power which is used within the home or passed back to the national grid. This is passed back power is referred to as selling back.

With an off grid setup other than your solar panels you'd use some other source of secondary power for times when the sun's not shining. Options include a generator, wind turbine, hydro-power or battery backup each of these systems has its own pro's and con's but each situation for their use and or cost, duration, return on investment will differ. The main schematic difference between a grid and off-grid though is an off-grid generates DC power which it stores in batteries using a charger (the name of the charger will change depending on what your charging source is. A solar array uses a solar controller, wind and hydro both use controllers (in fact all 3 use the same model controller in different ways so if you have multiple sources of generation you will require multiple controllers) All these controllers essentially charge your batteries, one might say solar/charge controller or wind/charge controller. These batteries are used to provide power and flatten out the curves of either low power generation times or high power usage from multiple appliances all being used at the same time. The second part of an off-grid system is the generation of mains power onsite, rather than coming from the grid it is converted from DC power (the batteries power). This is just like the inverter used in a grid-tie setup to convert the solar DC power to mains AC power.

Difference between Grid-Tie and Off-Grid

In its simplest form "the grid" is the power grid that connects homes all over the country which provides them with mains power.

When you are connected to the mains power grid you are referred to as grid-tied or vice versa tied to the grid. So Off-Grid simply means operating your own power not tied to the nationwide grid.

When you go bush or remove yourself from your device people quite often refer to this as going-off-the-grid. Not quite the same but it might be where some people associate off-grid with being remote or removed. It doesn't mean without technology though as a modern-day off-grid setup can actually be smarter and more intuitive than your current smart meter.

In-fact building your own power source with battery backup, solar and grid independence gives your location the ability to store, sell, distribute, manage, monitor, and action your power in almost unlimited ways. All with the benefit of resilience to outside infrastructure, outages, or scheduled power cuts. The components and hardware used in grid and off grid should be from a quality internationally recognised brand as the hardware should be assessed as a system costs that you can calculate over a 20 year period for a good return on your investment.

There is another variation from grid or off-grid. It's really a hybrid of the two systems taking the best of both and in recent years its becoming more and more common. Grid-tied with battery backup has been around for some 15+ years but marketing by Telsa and the Teslawall has made everyone aware of its existence. LG chem and others have similar "wall" designs which give people options for internal or external system storage designs.

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